Analysis And Application O The Thread Connection Quality And Tightening Process Of Automobile

Thread connection is the most commonly used connection method during vehicle assembly.Although the thread fastener is small,as the important connection component,its connection quality directly affects the reliability of the vehicle.The thread connection structure of some key components is more related to the safety performance of the vehicle.Therefore,the quality of thread connections has been increasingly concerned by domestic and foreign automobile manufacturers and component manufacturers.Based on the mechanical principle of thread connection,the mechanical relationship of thread connection,the influence of friction coefficient on thread connection,and the principle of control of pretension are expounded in this paper.Based on this mechanical principle,the method of optimizing the quality of the thread connection is studied from two aspects: thread loosening mechanism and thread tightening process control.Finally,based on the theoretical and experimental research results,the thread connection structure of a battery pack of battery electric vehicle was optimized and improved.The main research results are as follows:(1)It is found that the friction coefficient has a great influence on the quality of thread joint.Because the friction coefficient is excessive,not only the pretension obtained by the threaded fastener is reduced,but also the yield stress of the threaded fastener is reduced;(2)Through mechanical analysis,it is found that many factors such as pretension,equivalent friction diameter,pitch,plastic deformation,and temperature change will affect the quality of the screw connection.And,in the residual torque detection method of the production process,the attenuation of the thread torque can be more intuitively demonstrated by using the tightening method compared with the loosening method;(3)Through finite element analysis,it is found that when the bolts in a in-line arrangement and a rectangular arrangement cannot be tightened simultaneously,tightening from the inside to the outside and tightening diagonally will make the overall quality of the bolt tightening better;(4)It is proposed to improve the quality of the tightening of threaded fastener by establishing a tightening process monitoring window based on the 6Sigma theory.And it is confirmed by the experimental analysis that the torque monitoring window of the torque angle method established by this method can identify the difference in frictioncoefficient between the thread fasteners.